Patent GB-1388017-A (GB)
Title: Stepping motor control device
IPC: H02P8/14
Filed: 1972-02-22
Abstract: 1388017 Control of stepping motors HONEYWELL INFORMATION SYSTEMS ITALIA SpA 22 Feb 1972 [22 Feb 1971] 8193/72 Heading H2J A control system for a stepping motor comprises means to generate a sequence of primary pulses each representing a different angular position of the rotor of the motor between two consecutive stepping positions thereof, means to produce during each primary pulse sequence an additional pulse which is delayed with respect to a predetermined primary pulse in the sequence and means responsive to the primary pulses and the additional pulse to switch energizing currents of the motor windings so as to provide braking and subsequent holding torques to bring the motor to a predetermined stopping position. In the described embodiment the additional pulse changes the energization from a braking to a holding torque at an instant dependent on the speed of the rotor, whereby it is brought to its stopping position rapidly and without hunting.   The control system shown in Fig. 2 comprises an arrangement of gates, flip-flops, one-shot multivibrators, amplifiers and inverters, of which members 5 ... 8 receive the output pulses F<SP>1</SP> ... F 6  (Fig. 3) of a photodiode or phototransistor 4 illuminated by a photoemitter 2 through the transparent windows of a track a (Fig. 3) on a disc 3 mounted on the rotor, the windows being arranged to cause stopping of the motor at positions P 0 , P 2 , P 4  and to prevent stopping (or initiate an alarm) at positions P 1 , P 3 . The pulses F 1  ... F 6  are passed to a counter and decoder circuit 10, which produces on its output terminals 11 ... 15 corresponding pulses D 1 , D 3  ... D 6  of which D 1 , D 3 , D 4  are used to control the motor in its step-by-step mode, D 1  and D 4  are used for control in the slew mode, D 5  counts the member of steps moved and D 6  is used only during the slew mode of operation. A logic control circuit 30 receives input commands AP x IP x AR x IR x  respectively producing forward and backward step-by-step motion and forward and backward slew motion. Lead 16 of circuit 30 supplies a pulse D 0  for starting the motor and a one-shot multivibrator 42 supplies a pulse D, which follows the pulse D 4  after a delay R 1  determined by another oneshot multivibrator 41. Pulse D 0  sets a flip-flop 23 also controlled by pulses D 4 . Another flipflop 22 receives the pulses D 1  and D 7  and the two are alternately set and reset, flip-flop 22 under the control of pulses D 1  and flip-flop 23 under the control of pulses D 0  and D 4 . The flip-flops control, via AND gates 54 ... 57, transistors 27, 27<SP>1</SP>, 28, 28<SP>1</SP> switching the motor windings AM. In a typical step-by-step operation shown between positions P 0  and P 2  in Fig. 3, the pulses D 0 , D 1  and D 3  cause switching between the torque waveforms C 10  and C 11 . the changeover between these two torques being made before the maximum torque value to take into account the delay caused by winding inductance on the flux switching in the stator pole-pieces. After acceleration on torque waveforms C 10 , C 11  and braking on waveform C 10 , the pulse D 7  produces a change from the latter to a holding torque on the waveform C 11 . The speed of the motor determines the position of pulse D, relative to the waveforms C 10 , C 11  whereby the braking action is prolonged or shortened according to whether the speed is too high or too low. It is also explained, Fig. 5 (not shown), how the holding torque varies with the speed and how the rotor may be stopped without hunting by suitable choice of the pulse D 4  and delay time R 1 . In a typical slew operation, Fig. 4 (not shown) the pulses D 1 , D 4  produce switching between the torque waveforms to produce a positive torque for acceleration to a maximum speed, whereupon pulse D 5  is applied to circuit 30 to count the number of steps travelled. At a predetermined number in advance of the final desired stopping position, operation is transferred to switching between the torque waveforms to produce a negative (braking) torque, at the beginning of which action pulses D 1 , D 3 , D 4 , D 6  are passed to a multivibrator 49, which produces an output to de-energize the windings AM when the speed has fallen to a predetermined value (set by the multivibrator characteristic). A further multivibrator 52 monitors the further fall in speed due to friction and permits reenrgization of the windings in the step-by-step mode (set up at the beginning of de-energization) when the speed has fallen to another predetermined value. The subsequent control using the pulses D 1 , D 3  D, is identical to that already described for the step-by-step operation in Fig. 3. Members 60 ... 63 provide an alarm signal or cause further motor movement, if the disc 3 stops in a position such that the photo-detector 4 is illuminated. Other arrangements of window track to produce travel steps corresponding to one, three or four rotor step(s) are described, Figs. 6 and 7 (not shown). Modifications to the operation during the slew-mode are also envisaged, for example using various combinations of accelerating, braking and de-energizing stages.